The transient entanglement networks of cellulosic polysaccharides in concentrated solutions were characterized by the molecular weight between entanglements (M e) using dynamic viscoelasticity measurements. From the concentration dependence ofM e, M e for the cellulosic polysaccharides in the molten state (M e, melt) was estimated as the material constant reflecting the chain characteristics. The values of M e, meltwere compared among three cellulosic polysaccharides: cellulose, methylcellulose, and hydroxypropyl cellulose. Methylcellulose and hydroxypropyl cellulose were employed as cellulose derivatives having small and large side groups, respectively. It appeared that hydroxypropyl cellulose had significantly larger M e, melt compared with cellulose and methyl cellulose. However, the numbers of repeating glucose-ring units between entanglements were very close to each other among the three polysaccharides.